Thread Content
Material and material fatigue wear are related to each other; under prolonged exposure to impacts, friction, vibrations, and airflow-induced wear, the various properties of any material undergo significant changes. Its hardness, strength, toughness, as well as its wear and corrosion resistance decrease, to the point where it can no longer function properly. Everything on Earth is in motion, and where there is motion, there is wear and tear. In the petrochemical industry, metal smelting, industrial and mining ports, as well as in automation and transmission equipment, there are various types of tower fans, impellers, pumps, conveyance pipelines, metal sheets, and components for various devices. These elements not only operate in highly corrosive environments but are also constantly subjected to friction and impact from moving media, enduring the effects of impacts and wear caused by different types of media. Its surface wears down rapidly, and may even peel off, after being subjected to prolonged impact and mechanical stress; this results in a loss of its protective function over the substrate, affecting the quality and lifespan of the equipment. Furthermore, these components are usually not removable, making it very difficult to repair the surface; in some cases, it is even impossible to carry out any repairs. In response to this situation, the research and development of high-strength wear-resistant materials have never ceased. As is well known, epoxy resins possess good chemical resistance, particularly outstanding alkali resistance. They offer excellent adhesion to various substrates, as well as great toughness, hardness, and flexibility. Their good water resistance makes them widely used in coating materials, and they are already employed extensively in industry. However, due to the formation of a dense aromatic structure after curing, along with high cross-linking density and strong cohesion, their ability to deform is limited, resulting in a brittle nature. Coatings made from these resins often fail to meet the required performance standards, especially at higher temperatures. To further improve the various properties of wear-resistant coatings, Normack in Canada has, through decades of research, improved polyurethane wear-resistant materials. The spray-type polyurethane elastomers resulting from these efforts exhibit significantly enhanced wear and corrosion resistance, as well as improved elasticity, toughness, and adhesion. From a molecular structure perspective, spray-applied polyurethane elastomers are block polymers; their molecular chains generally consist of two parts, with one part being in a highly elastic state at room temperature, and this part is known as the soft segment ； The other portion is in a glassy or crystalline state, and is referred to as the hard segment. Generally, the soft segments are composed of flexible long chains of polymeric polyols, while the hard segments are made up of isocyanates and chain extenders; these soft and hard segments alternate with each other, thereby forming repeating structural units. In addition to the urethane groups, the main chain of polyurethane molecules also contains polar groups such as ethers, esters, or urea groups. Due to the presence of a large number of such polar groups, hydrogen bonds can form within and between polyurethane molecules. The thermodynamic incompatibility between the soft segments and the hard segments leads to the formation of microdomains of each type, resulting in a microphase-separated structure. Even linear polyurethanes can undergo physical cross-linking through hydrogen bonds. These structural features endow polyurethane elastomers with excellent wear resistance and toughness, earning them the reputation of being \"wear-resistant rubbers\". Hydrogen bonds exist between groups containing highly electronegative nitrogen and oxygen atoms as well as groups containing hydrogen atoms; the strength of these bonds is related to the cohesive energy of the groups. The urethane and urea groups in the rigid segments have strong polarity, and hydrogen bonds primarily form between these segments. It is reported that most of the imine groups among the various functional groups in polyurethane macromolecules can form hydrogen bonds; the majority of these bonds are formed between imine groups and carbonyl groups in the hard segments, while a smaller portion is formed between imine groups and ether oxygen atoms or ester carbonyl groups in the soft segments. The strength of hydrogen bonds is much weaker compared to the bond strength of intramolecular chemical bonds. However, the presence of a large number of hydrogen bonds is also one of the important factors affecting the properties of polar polymers. Hydrogen bonds are reversible; at lower temperatures, the tight arrangement of chain segments facilitates the formation of hydrogen bonds. At higher temperatures, the segments gain energy and undergo thermal motion, increasing the distance between them and the molecules, which weakens or even eliminates the hydrogen bonds. Hydrogen bonds act as physical cross-links, enabling polyurethane materials to possess high strength, wear resistance, solvent resistance, and low tensile set. The more hydrogen bonds there are, the stronger the intermolecular forces, and the higher the strength of the material. The amount of hydrogen bonding directly affects the degree of microphase separation in the system. Sprayed polyurethane elastomer wear-resistant materials are widely used in industries such as mining, the automation sector, sewage treatment, water management, food processing, and healthcare, thanks to their excellent physical and chemical properties, simple application process, and environmental friendliness with no pollution.